This invention relates to the treatment of metal surfaces to increase their resistance to corrosion. It further relates to compositions which form a corrosion-resistant film on metal surfaces to which they are applied. In a specific embodiment, the invention relates to corrosion-inhibiting treatment of downhole surfaces of oil-drilling equipment. In a further specific embodiment, the invention relates to corrosion-inhibition in oil recovery operations involving the use of polymeric agents.
The problem of corrosion of metal surfaces in contact with air and water is well known. Corrosion and pitting are accelerated in environments in which metal surfaces are in contact with corrosive chemicals such as hydrogen sulfide, carbon dioxide and organic acids, and water having a high electrolyte concentration. Such environments are typical of downwell conditions in oil and gas wells, in which corrosion of metal pipes, pumps and other equipment poses a serious problem requiring monitoring of well sites, frequent maintenance and costly replacement of parts. Oil recovery operations in deep-sea oil fields present these corrosion problems in their most extreme form. The downwell metal surfaces are in contact with large quantities of corrosive chemicals such as dissolved acid gases present in the recovered oil, and the metal surfaces are subjected to temperatures of 90.degree. C. or higher and pressures of 1000 psig or higher, the extreme conditions of temperature and pressure acting to accelerate corrosion and to intensify the problems of applying and maintaining chemical protection for the equipment.
Conventional corrosion-inhibiting agents are often not effective at all under such extreme conditions or reduce corrosion significantly for only a short period of time and then must be reapplied, often at great expense and inconvenience if the well site is not easily accessible or, as in the case of offshore wells, poses difficulties of transporting and applying large volumes of chemicals. In post-primary oil recovery operations involving the use of break-through polymers, severe corrosion on downwell equipment and tubing can result from the incompatibility of some conventional corrosion-inhibiting agents with the break-through polymers.
It has been found that certain chemical agents containing mercaptan groups are effective in inhibiting corrosion. However, the use of effective amounts of such mercaptans poses severe problems of human handling and application because of the intolerable odor of such chemicals.
It is therefore an object of this invention to provide a composition which can be applied to a metal surface to inhibit corrosion and pitting on the metal. It is a further object of the invention to provide a method of treating metal surfaces so as to form a film which inhibits corrosion on the metal even under extreme conditions of temperature and pressure and in highly corrosive environments. It is a further object of the invention to provide a composition and method of treating downwell metal surfaces of oil drilling equipment and tubing. It is a further object to provide a corrosion-inhibiting composition based on a sulfur-containing material which composition is relatively free of characteristic mercaptan odors. It is a further object of the invention to provide a composition and method for treating downwell surfaces of oil drilling equipment and tubing in an oil recovery environment which includes polymeric permeability control agents.